The present invention relates generally to a sensor, and more particularly to a sensor for detecting presence of a sheet while the sheet which is being advanced or conveyed on a photoreceptor of a xerographic device such as a photocopier, printer, or similar type device.
Sensors have heretofore been designed which are adapted to detect presence of a sheet which is being advanced or conveyed on a photoreceptor, such as when the sheet is tacked to the photoreceptor due to electrostatic forces during a xerographic printing process. Such sensors are positioned along the path of travel of the photoreceptor and function to sense the presence or absence of a sheet positioned on the photoreceptor in order to detect appropriate or inappropriate movement of the sheet within the xerographic device.
One example of the above type of sensor utilizes a light transmitter and associated detector. Movement of the sheet into the path of travel of the light generated by the light transmitter causes a difference in the amount of light being received by the light receiver. As a result, presence of the sheet may be detected.
However, there are disadvantages of a sensor which utilizes a light transmitter and associated receiver. For example, accumulation of dust and other particulate material on the light transmitter and receiver tends to inhibit proper functioning of the sensor. Moreover, a sensor which utilizes a light transmitter and associated detector may not be effective to detect the presence of a sheet which is transparent or translucent. In addition, if a photoreceptor has a patch of toner (e.g. a process control patch) positioned thereon which is a bright color such a yellow, the above type of prior art sensor may inappropriately generate a control signal indicating that a sheet is present in response to such control patch being advanced by such sensor on the photoreceptor. Further, if a sheet is being transported on the photoreceptor during a duplex printing job and the backside of the sheet has a dark color toner such as black or brown adhered thereto, the above type of prior art sensor may inappropriately generate a control signal indicating that no sheet is present on the photoreceptor since the presence of the black or brown toner on the backside of the sheet may cause such sensor not to detect the presence of the sheet.
Still another disadvantage of this type of sensor is that light generated by the light transmitter may adversely affect the electrostatic charge carried by the photoreceptor and/or the sheet being advanced thereon. Indeed, such light may dissipate the electrostatic charge on the photoreceptor and/or sheet thereby interfering with the xerographic process.
What is needed therefore is a sheet sensor which addresses one or more drawbacks of the previously designed devices. For example, what is needed is a sheet sensor which detects presence of a sheet which is being advanced or conveyed on a photoreceptor but yet does not utilize a light transmitter and receiver.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 3,479,026
Patentee: Plummer et al.
Issued: Nov. 18, 1969
U.S. Pat. No. 3,603,680
Patentee: Barton
Issued: Sep. 17, 1971
U.S. Pat. No. 4,066,969
Patentee: Pearce et al.
Issued: Jan. 3, 1978
U.S. Pat. No. 4,513,404
Patentee: Huggins
Issued: Apr. 23, 1985
It is a feature of the present invention to provide a new and useful sheet sensor.
It is another feature of the present invention to provide an improved sheet sensor.
It is yet another feature of the present invention to provide a sheet sensor adapted to detect presence of a sheet which is being advanced or conveyed on a photoreceptor which does not utilize a light transmitter and associated receiver.
Other feature and benefits of the present invention can be discerned from the following description and accompanying drawings.
In accordance with one embodiment of the present invention, there is provided a method which includes placing a vibratory member in contact with an imaging member. The method further includes applying an input signal to the vibratory member so as to excite the vibratory member and impart vibrations to the imaging member. In addition, the method includes determining if a current level of the input signal falls below a threshold value and generating a control signal in response thereto.
Pursuant to another embodiment of the present invention, there is provided a sensor for detecting presence of a sheet which is being advanced on a photoreceptor of an electrophotographic printing device. The sensor includes a vibratory member which is configured to be positioned in contact with the photoreceptor. The sensor further includes a drive circuit operable to generate an input signal on a signal line which is coupled to the vibratory member. The sensor additionally includes a sensing circuit operable to (i) determine if a current level of the input signal falls below a threshold value, and (ii) generate a control signal in response thereto.
According to still another embodiment of the present invention, there is provided a printing machine which includes a charge retentive member configured to be advanced in a path of movement. The printing machine further includes a sensor operable to detect presence of a sheet which is being advanced on. the charge retentive member. The sensor includes (i) a vibratory member positioned in contact with the charge retentive member, (ii) a drive circuit operable to generate an input signal on a signal line which is coupled to the vibratory member, and (ii) a sensing circuit operable to monitor electrical characteristics of the input signal and generate a control signal in response to the electrical characteristics possessing a predetermined quality.